Heat stable SnAl and SnMg based dielectrics

ABSTRACT

A transparent dielectric composition comprising tin, oxygen and one of aluminum or magnesium with preferably higher than 15% by weight of aluminum or magnesium offers improved thermal stability over tin oxide with respect to appearance and optical properties under high temperature processes. For example, upon a heat treatment at temperatures higher than 500 C, changes in color and index of refraction of the present transparent dielectric composition are noticeably less than those of tin oxide films of comparable thickness. The transparent dielectric composition can be used in high transmittance, low emissivity coated panels, providing thermal stability so that there are no significant changes in the coating optical and structural properties, such as visible transmission, IR reflectance, microscopic morphological properties, color appearance, and haze characteristics, of the as-coated and heated treated products.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Continuation Application of U.S. patent application Ser. No.13/305,550, now issued as U.S. Pat. No. 8,784,934, filed Nov. 28, 2011,which is herein incorporated by reference for all purposes.

FIELD OF THE INVENTION

The present invention relates generally to films providing hightransmittance and low emissivity, and more particularly to such filmsdeposited on transparent substrates.

BACKGROUND OF THE INVENTION

Sunlight control glasses are commonly used in applications such asbuilding glass windows and vehicle windows, typically offering highvisible transmission and low emissivity. High visible transmission canallow more sunlight to pass through the glass windows, thus beingdesirable in many window applications. Low emissivity can block infrared(IR) radiation to reduce undesirable interior heating.

In low emissivity glasses, IR radiation is mostly reflected with minimumabsorption and emission, thus reducing the heat transferring to and fromthe low emissivity surface. Typical sunlight control glasses havegenerally an emissivity of about 0.1 and a light transmission of about80%. High transmittance, low emissivity glasses generally include areflective metal film to provide infrared reflectance and lowemissivity, which is sandwiched between antireflective films to reducethe visible reflectance.

In certain cases, the glasses are heat treated for tempering, bending orstrengthening, requiring the use of temperatures of 500 C or higher. Theheat treatment process can affect the coatings, such as deterioration,structural or color changes, or become hazy following the heattreatment, exhibiting a reduction in visible transmission andsignificant color changes.

SUMMARY

In some embodiments, the present invention discloses a transparentdielectric composition comprising tin, oxygen and one of aluminum ormagnesium with higher than 2.5% by weight, and preferably higher than15% by weight of the total metal weight. The present transparentdielectric composition can offer improved thermal stability over tinoxide and other dielectric materials with respect to appearance andoptical properties under high temperature processes, includingreflective and transmittive optical properties. For example, upon a heattreatment at a temperature higher than 500 C, changes in color and indexof refraction of the present transparent dielectric composition arenoticeably less than those of tin oxide films of comparable thickness.Further, the present composition can offer minimum structural changes,including possessing an amorphous structure that is stable upon the hightemperature process. In some embodiments, the present transparentdielectric composition comprises less than 70% by weight of aluminum ormagnesium with respect to the total metal weight in the composite film;and preferably comprises less than 35% by weight.

In some embodiments, the present invention discloses a method and a hightransmittance, low emissivity coated panel fabricated from the method,wherein the panel comprises a transparent substrate coated with atransparent dielectric film comprising tin, oxygen and one of aluminumor magnesium present in amounts higher than 2.5% by weight andpreferably higher than 15% by weight. The coated panel can be used aslow emissivity transparent substrates, offering improved thermalstability, for example, as compared with tin oxide coatings with regardto structural and optical property changes upon high temperatureprocesses. The transparent dielectric film can be coated on glass orplastic substrates, offering low emissivity properties together withminimal variations after high temperature processes.

In some embodiments, the high transmittance, low emissivity coated panelfurther comprises other layers, such as a metallic reflective film, anantireflection layer, and a coating protection layer, together with asequence of repeated multilayers.

In some embodiments, the present invention discloses a transparentdielectric layer serving as a thickness optical filler, which comprisestin, oxygen and one of aluminum or magnesium. To improve thetransmittance, the thicknesses of the coated layers are normallypreferred to be as thin as possible. However, in certain cases, a fixedthickness is desirable, for example, to achieve destructiveinterferences in the beams reflected from the interfaces, andconstructive interference in the corresponding transmitted beams. Sincethe present transparent dielectric layer possesses improved color andoptical properties with respect to high temperature process, it canserve as a thickness optical filler for coated panels, preserving itsproperties after the high temperature process.

BRIEF DESCRIPTION OF THE DRAWINGS

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. The drawings are not to scale and the relative dimensionsof various elements in the drawings are depicted schematically and notnecessarily to scale.

The techniques of the present invention can readily be understood byconsidering the following detailed description in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates an exemplary thin film according to an embodiment ofthe present invention.

FIG. 2 illustrates an exemplary deposition configuration according to anembodiment of the present invention.

FIGS. 3A and 3B illustrate exemplary changes in index of refraction forSn—Mg—O and Sn—Al—O systems.

FIGS. 4A-4C illustrate exemplary coating layers on transparent panels.

FIGS. 5A-5B illustrate exemplary processes for provide thermal stablecoatings.

DETAILED DESCRIPTION

A detailed description of one or more embodiments is provided belowalong with accompanying figures. The detailed description is provided inconnection with such embodiments, but is not limited to any particularexample. The scope is limited only by the claims and numerousalternatives, modifications, and equivalents are encompassed. Numerousspecific details are set forth in the following description in order toprovide a thorough understanding. These details are provided for thepurpose of example and the described techniques may be practicedaccording to the claims without some or all of these specific details.For the purpose of clarity, technical material that is known in thetechnical fields related to the embodiments has not been described indetail to avoid unnecessarily obscuring the description.

The invention relates to materials for transparent and low emissivecoatings and to coated transparent panels, such as glass panels, withimproved thermal stability. The coated transparent panels can comprise atransparent substrate having one or more transparent low emissivecoatings. Such panels offer high transmission of visible light with highthermal reflectance, and generally comprise an infrared (IR) reflectinglayer embedded between transparent antireflection layers.

The coated glass panels sometimes are desired to be heat treated, e.g.,to toughen the glass substrate or to ease bending in various areas ofapplications. The substrates are typically heated to a temperature nearor above the softening point and then toughened by rapid cooling orbending them to appropriate shapes. For example, tempered glass can bestronger than annealed glass, and can shatter into small pieces whenbroken. The temperature range for glass heat treatment is typicallybetween 500 and 900 C, with a processing time of several minutes, e.g.,between 5 to 10 minutes.

In some embodiments, the present invention provides a heat treatabledielectric low emissive coating, and corresponding coating stacks, whichare thermally stable with minimal changes before and after a heattreatment, so that non-heat treated and heat treated substrates can bestocked interchangeably. Preferably, the heat treatment does not cause asignificant change in the coating optical and structural properties,including reflective and transmittive optical properties, such asvisible transmission, IR reflectance, microscopic morphologicalproperties, color appearance, and haze characteristics. For example, thepresent coated transparent panels have reduced changes in appearanceupon a heat treatment, such as a color difference that can be detectedby visual inspection.

The coated transparent panels can comprise a glass substrate or anyother transparent substrates, such as substrates made of organicpolymers. The coated transparent panels can be used in windowapplications such as vehicle and building windows, skylights, or glassdoors, either in monolithic glazings or multiple glazings with orwithout a plastic interlayer or a gas-filled sealed interspace.

Heat treatments of coated glass panels can generate some complications,such as changes in structural properties and color between non-heattreated and heat treated products, for example, upon heating of thecoated glass, a color change can be observed, making the as-coatedproduct and heat treated (tempered) product different in appearance.

In some embodiments, the present invention discloses materials, thinfilms, and processes that provide the coated panels with similar or samestructures and appearance for as-coated and tempered products. In someembodiments, the present invention discloses coated panels where each ofthe individual layers in the coated stack is thermally stable and theinteraction between layers is minimized during heating. The presentcoatings can be subjected to prolonged high temperature heat treatmentswithout damaging the coated panels, with minimal property changes, suchas light transmittance, IR reflection, structure and color appearance.In addition, the present coatings can protect the IR reflecting layersduring the high temperature process, such as preventing oxidation oragglomeration of the IR reflective layer.

In some embodiments, the present invention discloses a transparentdielectric composition comprising tin, oxygen and one of aluminum ormagnesium, which can offer improved thermal stability such as colorappearance (e.g., reflective optical property) or transmittive opticalproperties (e.g., transparency) under high temperature processing. Thehigh temperature processing can comprise an annealing at temperaturehigher than 500 C. For example, upon a heat treatment in a prolongedhigh temperature process, minimal changes in color and index ofrefraction of the present transparent dielectric composition areobserved, wherein the changes are noticeably less than other transparentfilms, such as tin oxide films of comparable thickness. Further, thepresent composition can offer thin films having an amorphous structure,which is stable upon the high temperature process, and thus providingsimilar structural properties for heat treated and non heat treatedproducts. Also, the amorphous structure can offer ease of glassprocessing, such as bending or shaping.

In some embodiments, the compound material has a composition ofmagnesium or aluminum of 2.5% or greater, preferably between 2.5% and5%, and more preferably 15% or greater by weight of the total metalweight. The magnesium or aluminum composition is further preferably lessthan 70% by weight, and more preferably less than 35% by weight. In thepresent description, the weight percentage is defined as the weightpercentage of the added element from the total metal weight. Forexample, in a tin magnesium compound, the weight percent of magnesium Mg% is expressed as a ratio of the weight of magnesium W_(Mg) over thetotal weight of magnesium W_(Mg) and tin W_(Sn):

${{Mg}\mspace{14mu}\%} = {100 \times \frac{W_{Mg}}{W_{Mg} + W_{Sn}}}$

The weight of non metal elements, for example, oxygen in tin magnesiumoxide compounds, is not considered in the weight percentagecalculations. For example, 15% by weight of magnesium in a tin magnesiumoxide compound material is defined as the weight of magnesium being 15%of the total weight of tin and magnesium.

The present coating can be useful in different thickness ranges. In someembodiments, the present coatings can be used as an optical filler,providing the necessary optical thickness for the whole coating stack.In certain cases, the total thickness of the coating stack ispredetermined, for example, a half wavelength thickness forantireflection purpose. Further, the active layers, such as the IRreflective coating of silver, is preferably as thin as possible, inorder to not affect the visible light transmission property. Thus, insome embodiments, the present compound material can be used as anoptical filler, providing the necessary thickness for the coated panelsto effectively anti-reflect the IR radiation, while satisfying otherrequirements such as structural and color stability upon hightemperature processing. The thickness can be less than 100 nm, andpreferably less than 8 nm.

In some embodiments, the compound material comprises a tin magnesiumoxide (Sn—Mg-Oxide) or tin aluminum oxide (Sn—Al-Oxide) system, having amixture of tin oxide with one of magnesium or aluminum. The mixture canbe a tin oxide doped with magnesium or aluminum. The mixture can also bean oxide alloy of tin with magnesium or aluminum. Further, the mixturecan have different forms on the microscopic level, and in the context ofthe invention, comprising atoms of tin, oxygen and magnesium oraluminum, regardless of how they are bound to each other on themicroscopic level. In some embodiments, the mixture of tin oxide witheither magnesium or aluminum is proven to be suitable for a transparentcompound layer with thermal stability properties, in addition to havinghigh light transmittance and low thermal energy transmittance.

In some embodiments, the present transparent low emissive coating is anessentially homogeneous layer, such as having an amorphous structure.Such amorphous structure is preferred, but not absolutely necessary,since amorphous structures tend to have smaller grain growth compared tocrystalline structures, thus can offer more stable structure, e.g.,minimal structural changes, upon high temperature processing. Forexample, the present doped tin oxide remains amorphous with minimumstructural changes after a high temperature treatment, as compared totin oxide, which is a commonly used dielectric layer in the low emissivestack, exhibiting high grain growth, together with changes in opticalproperties, such as refractive index n and extinction coefficient kafter similar heat treatment. In some embodiments, the present inventiondiscloses alloying tin with another metal, for example, by reactivesputtering, to stabilize the dielectric properties during the heattreatment. For example, the alloying metal can be aluminum or magnesiumwith 2.5% or higher, preferably 15% or higher, by weight of aluminum ormagnesium with respect to the total weight of tin and aluminum ormagnesium, respectively. Tin aluminum oxide and tin magnesium oxide withmore than 15% aluminum or magnesium by weight shows improved overallproperties after a heat treatment, compared to pure tin oxide, includinga stable structure, as determined by x-ray diffraction (XRD) spectrabefore and after the heat treatment, and smaller changes in opticalproperties as compared to tin oxide.

In some embodiments, the present composition allows a single product, interms of minimal or no color change between as-coated and temperedglasses, avoiding the need for different stack designs used to match thecolor between as-coated and heat treated products. The presentcomposition can be used in thin film coatings for transparentsubstrates.

FIG. 1 illustrates an exemplary thin film coating according to someembodiments of the present invention. The present transparent dielectricthin film 22 is disposed on a transparent substrate 21 to form a coatedtransparent panel 20, which is thermal stable, in addition to otherfunctional and appearance properties, such as high visible lighttransmission, and low IR emission. The thermal stability of the presentpanels provides similar structural, optical and visible appearanceproperties for as-coated and heat treated panels, allowing ease ofwindow and door designs and stockage.

The compound layer 22 can be deposited using different processes andequipment, for example, physical vapor deposition (PVD) or chemicalvapor deposition (CVD), with sputtering processes preferred. The targetscan be sputtered under direct current (DC), pulsed DC, alternate current(AC), radio frequency (RF) or any other suitable conditions. In someembodiments, the present invention discloses a physical vapor depositionmethod for depositing the transparent dielectric film which comprisestin, oxygen and one of aluminum or magnesium. In some embodiments, themethod comprises supplying a gas mixture into a processing chamber, andsputtering material from one or more targets disposed in the processingchamber, wherein the targets comprise tin and one of aluminum ormagnesium. In some embodiments, the process further comprises reactingthe sputtered material with the gas mixture comprising oxygen. Thesputtering process can utilize different target configurations, such asone target having tin, oxygen, and one of aluminum or magnesium; onetarget having tin, and one of aluminum or magnesium, with oxygenintroduced from the reactive gas mixture; and two targets with onetarget comprising tin and the other target comprising one of aluminum ormagnesium, with oxygen introduced from the reactive gas mixture. Othertarget configurations can also be used, such as a tin oxide targettogether with a target comprising one of aluminum or magnesium. Thesputtering process can further comprise other components such as magnetsfor confining the plasma, and utilize different process conditions suchas DC, AC, RF, or pulse sputtering. In some embodiments, the compoundmaterial is an essentially homogeneous layer, formed by sputterdeposition from targets comprising tin and (magnesium or aluminum) in anoxygen-containing sputtering ambient.

FIG. 2 illustrates an exemplary deposition configuration according tosome embodiments of the present invention. A sputter deposition chamber30 comprises two targets 31A and 32B disposed in a plasma environment34, containing reactive species delivered from an outside source 32. Thetargets 31A and 31B can comprise tin and one of magnesium or aluminum,together with the reactive species of oxygen to deposit a mixture oftin, magnesium or aluminum, and oxygen to form a magnesium or aluminumdoped tin oxide layer on substrate 33. This configuration is exemplary,and other sputter system configurations can be used, such as a singletarget comprising tin-magnesium or tin-aluminum alloy, or a ceramictarget comprising tin-magnesium-oxide or tin-aluminum-oxide.

To assess the deposited compound layer properties, tests were performedusing high temperature heat treatment of above 500 C for more than 5-10minutes, to measure visual appearance and structure stability. The datawere then compared with non-heat treated samples, showing that the colorchange after a heat treatment of the product is less than with tinoxide, and the structure of the deposited layer remained amorphous (fromXRD spectra) after the heat treatment, allowing ease of glassprocessing, such as shaping and bending. Further, the stable structureand minimal color change allows for a single product for tempered andas-coated. The visible light transmittance property does not changeafter a heat treatment, and is similar to comparable state-of-the-artmaterials, such as tin oxide.

FIGS. 3A and 3B illustrate exemplary changes in index of refraction forSn—Mg-Oxide and Sn—Al-Oxide systems according to some embodiments of thepresent invention. The figures show the percent changes in index ofrefraction for Sn—Mg-Oxide and Sn—Al-Oxide systems as a function ofweight percent of magnesium and aluminum, respectively. The changes inindex of refraction for Sn—Mg—O and Al—Sn—O are measured after a heattreatment process of 650 C for 8 minutes, using an ellipsometer withdifferent wavelengths of 400 nm and 550 nm. As shown, tin oxide filmsexhibit between 2% and 6% changes in index of refraction for thesewavelengths (see the graphs at zero weight percent of magnesium andaluminum). With increased doping of magnesium or aluminum, the changesare reduced, and at about 15% and more dopant concentration, the changesare minimized to about 1%.

These data, together with observed structural data, show thatSn—Mg-Oxide and Sn—Al-Oxide compositions with 15% or more by weight ofmagnesium or aluminum, respectively, exhibit minimal changes in visualappearance and properties after a prolonged high temperature heattreatment process. The present compositions of doped tin oxide with 15%or more magnesium or aluminum are thus suitable for use as dielectriccoatings in high transmission, low emissive transparent panels that areneeded to be similar in appearance and properties with or without a heattreatment process.

In addition, data show significant improvement for a smaller addition ofdopants, such as at 2.5% by weight or more of aluminum for Sn—Al-Oxidesystem. For example, FIG. 3B shows that the high temperature change inindex of refraction at 400 nm wavelength improves by a factor of 2(e.g., dropping from 5.2% to 2.6%). Thus data indicate that some thermalstability improvements can be accomplished with doping of 2.5% orgreater, for example, between 2.5% and 5% by weight aluminum ormagnesium in Sn—Al-Oxide or Sn—Mg-Oxide system.

In some embodiments, the present invention discloses a hightransmittance, low emissivity coated article, e.g., a panel, including atransparent substrate (such as a glass or plastic substrate) having atransparent dielectric coating of Sn—Mg-Oxide or Sn—Al-Oxide, preferablyhaving at least 15% by weight of magnesium or aluminum. In someembodiments, the concentration of magnesium or aluminum in Sn—Mg-Oxideor Sn—Al-Oxide system is 2.5% or greater, or preferably between 2.5% and5% by weight (including 5%). The magnesium or aluminum composition isfurther preferably less than 70% by weight, and more preferably lessthan 35% by weight. This layer can be used for blocking some infrared(IR) radiation while allowing a high percentage of visible lighttransmission. In some embodiments, the layer of Sn—Mg-Oxide orSn—Al-Oxide can be used as a dielectric layer in a low emissivitycoating, which can improve the thermal characteristics of such a lowemissive coating, for example, providing minimal structural or colorchanges upon high temperature processing. For example, color or opticalproperty of the present Sn—Mg-Oxide or Sn—Al-Oxide dielectric films canexhibit smaller changes after a high temperature process as compared tothose of tin oxide. In some embodiments, a dielectric interlayercomprising doped tin oxide with magnesium or aluminum can be providedtogether with an (IR) reflecting layer and other coating layers such asantireflective layer and protective layer.

The coated panels according to some embodiments of the invention can beheat treated (e.g., thermally tempered, heat bent and/or heatstrengthened), and still retain similar structure, optical and visualappearance as the non heat treated panels. For example, the structure ofthe present Sn—Mg-Oxide or Sn—Al-Oxide dielectric films is amorphousafter deposition, and remains amorphous after a high temperatureprocessing. The high temperature process, e.g., a heat treatment, cancomprise a high temperature anneal at 500 C or higher.

In some embodiments, the present invention discloses an improved coatedtransparent panel, such as a coated glass, that has acceptable visiblelight transmission and IR reflection, along with thermally stablecharacteristics after high temperature processing. The present inventionalso discloses methods of producing the improved, coated, transparentpanels, which comprise specific layers in a coating stack. One layercomprises tin oxide having a dopant such as magnesium or aluminum forreflecting thermal energy, such as midrange infrared light. In someembodiments, the coated transparent panels have a low haze value, beforeand after heat treatments. Haze can be due to the scattering of incidentlight, caused by surface roughness, for example, large crystalline size,different crystalline sizes or imbedded particles. By controlling themorphological structure, the present magnesium or aluminum doped tinoxide layer can have reduced haze values.

In some embodiments, multiple layer stacks and/or multiple lowemissivity layers can be utilized. In addition, the present inventioncontrols the thermal properties of the layer stack so that the opticaland structural properties of the heat treated and non heat treatedpanels are similar. In some embodiments, other coatings are selected tohave a high level of visible light transmittance, before and after aheat treatment. In some embodiments, the other layers can be any of thelayers well known in the art.

FIGS. 4A-4C illustrate exemplary coating layers on transparent panelsaccording to some embodiments of the present invention. FIG. 4A shows asimple coating stack for a surface coating of transparent substrate 21,such as a glass panel, comprising at least a doped tin oxide compositelayer 20 having a dopant of magnesium or aluminum. Relative to the totalamount, this dopant of magnesium or aluminum contains equal or greaterthan 2.5% (such as between 2.5% and 5%), and preferably equal or greaterthan 15% by weight of the metal content. The layer stack has an IRreflective layer, such as a silver layer 22, and the doped tin oxidecomposite layer 20 can be used as an upper antireflection layer, a lowerantireflection layer, a diffusion barrier layer, or an upper or lowercover layer. The doped tin oxide composite layers can be used with ametallic reflective layer, for example, as a bonding or antireflectionlayer, with the metallic reflective layer deposited on top, or as ablocker layer below the metallic reflective layers.

The present doped tin oxide layer can improve significantly the thermalstability and haze characteristics, together with possessing excellentstructural and optical properties for high transmittal, low emissivepanels, at least as compared to comparable tin oxide layers withoutmagnesium or aluminum dopants.

The layers of the invention may be used as a thin layer forantireflection, optical filler, or protective purposes, for example in athickness range of about 2 to 8 nm. Alternatively, the thickness may begreater, such as between 8 and 80 nm. In some embodiments, the presentinvention discloses a transparent dielectric layer serving as athickness optical filler, allowing the film stack to reach a desiredthickness. To improve the transmittance, the thicknesses of the coatedlayers are normally preferred to be as thin as possible. However, incertain cases, a fixed thickness is desirable, for example, to achievedestructive interferences in the beams reflected from the interfaces,and constructive interference in the corresponding transmitted beams.Since the present transparent dielectric layer possesses improved colorand optical properties with respect to high temperature process, it canserve as a thickness optical filler for coated articles, preserving itsproperties after the high temperature process.

In some embodiments, the present invention discloses a hightransmittance, low emissivity coated article comprising a transparentsubstrate, a metallic reflective film comprises one of silver, gold, orcopper; and a single transparent dielectric film of tin oxide alloysoverlying the substrate, the transparent dielectric film comprising tinoxide doped with aluminum or magnesium, and serving as a thicknessoptical filler for the metallic reflective film. The transparentdielectric film further exhibits smaller changes with regard to color oroptical properties after a high temperature process as compared to thoseof tin oxide.

In some embodiments, the present invention discloses a hightransmittance and low emissive layer stack in which a metallic IRreflective layer such as a thin silver, gold or copper layer, isembedded between two dielectric antireflection layers, at least one ofwhich is an oxidation product of tin and a dopant comprising one ofmagnesium or aluminum. In some embodiments, the overall optical andstructural properties of the doped tin oxide layer are stable afterincluding about 15% by weight dopant. In some embodiments, certainoptical or structural properties of the doped tin oxide layer areimproved after including about 2.5% by weight dopant, and thus smallerdopant percentages of 2.5% or greater can be used, depending on thespecific requirements of the layer stack. The thermal properties caninclude stable color and structure characteristics, such as minimumcolor and structure change upon high temperature processing. Forexample, the morphological structure of the present magnesium oraluminum doped tin oxide is amorphous, which is stable upon hightemperature processing, as compared to tin oxide with a polycrystallinestructure, which exhibits grain growth upon high temperature annealing.

While the inventive features of the present invention can be achievedwith two layers, multilayer embodiments are within the scope and contentof the invention. The multilayers can comprise additional hightransmittance, low emissivity layers or other functional or decorativelayers.

FIG. 4B illustrates an exemplary thin film stack according to someembodiments of the present invention. The thin film stack, disposed on atransparent substrate 51, comprises a metallic IR reflective layer 52sandwiched between two layers 50 and 53, wherein at least one of thesetwo layers 50 and 53 comprises a dielectric compound layer of magnesiumor aluminum doped tin oxide with at least 2.5%, preferably with at least15%, by weight dopant. In some embodiments, the dielectric compoundlayer is a high transmission layer with minimal visible lightreflection, comprising an alloy of tin and one of magnesium or aluminumthat has haze reducing characteristics. The other layer can be afunctional layer for low emissivity, such as an antireflective layer, asupport layer, such as a top protective layer or a seed layer for the IRreflective layer, or any other stack of layers having a thermal,optical, electrical function.

FIG. 4C illustrates a basic layer sequence incorporating the presentdoped tin oxide compound layer according to some embodiments of thepresent invention. A layer stack is disposed on a transparent substrate51, such as a glass substrate, which can be clear or tinted, monolithicor laminated. The thickness of the glass substrate depends on theapplications, and typically is between 1 and 20 mm. The transparentsubstrate can also be a polymer or plastic substrate.

A coating stack is provided on the substrate 51, either directly orindirectly, comprising multiple layers, some of which can be optional.The coating stack can comprise one or more antireflective films, ametallic IR reflective film comprising silver, gold or copper, and a topprotective film for protecting the coating stack.

In some embodiments, the coating stack can comprise a first dielectric,antireflective film stack on the substrate, including a single layer ormultiple layers for different functional purposes. For example, thefirst antireflective film stack can comprise a bottom dielectric layer54 for protecting the substrate, an antireflective layer 50, and acontact or seed layer 55 to facilitate the IR reflective layer 52.

The bottom dielectric layer 54 can comprise silicon nitride, siliconoxynitride, or other nitride material such as SiZrN, for example, toprotect the glass substrate or to improve the haze reduction properties.The antireflective layer 50 serves to reduce the reflection of visiblelight, selected based on transmittance, index of refraction, adherence,chemical durability, and thermal stability. In some embodiments, theantireflective layer 50 comprises magnesium or aluminum doped tin oxide,offering highly thermal stability properties, allowing the film stack topossess similar visual and functional properties before and after a heattreatment process. The antireflective layer 50 can comprise titaniumdioxide, silicon nitride, silicon dioxide, silicon oxynitride, niobiumoxide, SiZrN, tin oxide, zinc oxide, or any other suitable dielectricmaterial, for example, in some applications that do not require a highlevel of thermal stability.

The contact layer 55 can be used to provide a seed layer for the IRreflective film, for example, a zinc oxide layer deposited before thedeposition of a silver reflective layer can provide a silver layer withlower resistivity, which can improve its reflective characteristics. Thecontact layer can comprise nickel oxide, nickel chrome oxide, nickelalloy oxides, chrome oxides, or chrome alloy oxides.

On the first antireflective film stack is an IR reflective layer 52. TheIR reflective layer can be a metallic, reflective film, such as gold,copper, or silver. In general, the IR reflective film comprises a goodelectrical conductor, blocking the passage of thermal energy.

On the IR reflective layer 52 is a second antireflective film stack,including a single layer or multiple layers for different functionalpurposes. For example, the second antireflective film stack can comprisea top contact layer 56, a top antireflective layer 57, and topprotective layer 58 for protecting the total film stack. The top contactlayer 56 can be used to protect the IR reflective layer, such as aprimer film or an oxygen gettering film. The top contact layer cancomprise titanium, nickel or a combination of nickel and titanium. Theprotective layer 58 can be an exterior protective layer, such as siliconnitride, silicon oxynitride, titanium oxide, tin oxide, zinc oxide,niobium oxide, or SiZrN.

In some embodiments, the coating can comprise a double or triple layerstack, having multiple IR reflective layers.

In some embodiments, the present invention is also directed to a methodfor producing heat treated and non-heat treated coated transparentpanels wherein there are minimal changes in structure or colorappearance between two types of panels after being heat treated for lessthan 10-20 minutes at temperatures greater than 500 C.

FIGS. 5A-5B illustrate exemplary processes for provide thermally stablecoatings according to some embodiments of the present invention. In FIG.5A, a film stack comprising a tin oxide film alloyed with eithermagnesium or aluminum is used for a low emissive coating with highthermal stability. Operation 80 provides a transparent substrate, suchas a glass substrate or a plastic substrate. Operation 81 deposits atransparent dielectric film comprising tin oxide alloy over thesubstrate, wherein the tin oxide alloy comprises an alloy of tin oxidewith one of aluminum or magnesium, and wherein the amount of magnesiumor aluminum is at least 2.5%, preferably with at least 15%, by weight.The tin oxide alloy can be a high thermally stable film, allowing thecoated substrate to be similar in functions and appearance for as-coatedand heat treated products. For example, color or optical property of thepresent Sn—Mg-Oxide or Sn—Al-Oxide dielectric films can exhibit smallerchanges after a high temperature process as compared to those of tinoxide.

In FIG. 5B, another film stack comprising the present doped tin oxidefilm is used for a low emissive coating with high thermal stability,together with a metallic IR reflective layer and an optional protectivelayer. Other layers can be incorporated in the film stack such as anantireflective film. Operation 83 provides a transparent substrate.Operation 84 deposits a tin oxide alloy film over the substrate, whereinthe tin oxide alloy comprises an alloy of tin oxide with one of aluminumor magnesium, and wherein the amount of magnesium or aluminum is atleast 2.5%, preferably with at least 15%, by weight. The tin oxide alloyfilm can be used as an antireflective film for the film stack.Additional optional antireflective films can also be deposited.Operation 85 deposits a metallic reflective film. Operation 86 depositsa top film. The order of the film depositions can be different,depending on a particular film stack. In some embodiments, multiple filmstacks can be used.

The coated film stack can be heat treated, for example, annealing at atemperature higher than 500 C and less than 1000 C, for less than 10minutes. After the heat treatment, the coated film stack maintainssimilar appearance and properties as the unheated coated film stack. Insome embodiments, the coated film stack has improved appearance andproperties as compared to the unheated coated film stack, for example,as compared to prior art tin oxide antireflection coating.

Although the foregoing examples have been described in some detail forpurposes of clarity of understanding, the invention is not limited tothe details provided. There are many alternative ways of implementingthe invention. The disclosed examples are illustrative and notrestrictive.

What is claimed is:
 1. A film stack comprising: a first dielectriclayer, wherein the first dielectric layer consists of tin, oxygen, andone of aluminum or magnesium, wherein the aluminum or magnesiumcomprises more than 15% by weight of the total metal content of thecomposition of the first dielectric layer; a first reflective layerdisposed above the first dielectric layer, wherein the first reflectivelayer comprises silver; and a first barrier layer disposed above thefirst reflective layer, wherein the first barrier layer comprisesnickel, niobium, and titanium.
 2. A film stack as in claim 1, whereinthe aluminum or magnesium comprises less than 70% by weight of the totalmetal content of the composition of the first dielectric layer.
 3. Afilm stack as in claim 1, wherein a structure of the first dielectriclayer is amorphous.
 4. A film stack as in claim 1, further comprising asecond dielectric layer disposed above the first reflective layer,wherein the second dielectric layer consists of tin, oxygen, and one ofaluminum or magnesium.
 5. A film stack as in claim 1, wherein the filmstack is a transparent dielectric film stack, and wherein the film hasan appearance that remains the same, by visual inspection, after a heattreatment.
 6. A film stack as in claim 5, wherein the first dielectriclayer consists of tin oxide doped with one of aluminum or magnesium. 7.A film stack comprising; a dielectric layer, wherein the dielectriclayer consists of tin, oxygen, and one of aluminum or magnesium, whereinthe aluminum or magnesium comprises more than 15% by weight of the totalmetal content of the composition of the first dielectric layer; a seedlayer, disposed above the dielectric layer, wherein the seed layercomprises zinc oxide; a reflective layer disposed above the seed layer,wherein the reflective layer comprises silver; a barrier layer disposedabove the reflective layer, wherein the barrier layer comprises nickel,niobium, and titanium; and an overcoat layer disposed above the barrierlayer, wherein the overcoat layer consists of tin, oxygen, and one ofaluminum or magnesium.
 8. A film stack as in claim 7, wherein the filmstack is a transparent dielectric film stack, and wherein the film hasan appearance that remains the same, by visual inspection, after a heattreatment.
 9. A film stack as in claim 8, wherein the dielectric layerconsists of tin oxide doped with one of aluminum or magnesium.
 10. Afilm stack as in claim 7, wherein the dielectric layer consists of tinoxide doped with aluminum.
 11. A film stack as in claim 7, wherein thealuminum or magnesium comprises less than 70% by weight of the totalmetal content of the composition of the dielectric layer.
 12. A filmstack as in claim 7, wherein the dielectric layer consists of tin oxidedoped with magnesium.
 13. A film stack comprising: a first dielectriclayer, wherein the first dielectric layer consists of tin, oxygen, andone of aluminum or magnesium, wherein the aluminum or magnesiumcomprises more than 15% by weight of the total metal content of thecomposition of the first dielectric layer; a first seed layer, disposedabove the first dielectric layer, wherein the seed layer comprises zincoxide; a first reflective layer disposed above the first seed layer,wherein the first reflective layer comprises silver; a first barrierlayer disposed above the first reflective layer, wherein the firstbarrier layer comprises nickel, niobium, and titanium; a seconddielectric layer disposed above the first barrier layer, wherein thesecond dielectric layer consists of tin, oxygen, and one of aluminum ormagnesium; a second seed layer, disposed above the second dielectriclayer, wherein the seed layer comprises zinc oxide; a second reflectivelayer disposed above the second seed layer, wherein the secondreflective layer comprises silver; a second barrier layer disposed abovethe second reflective layer, wherein the second barrier layer comprisesnickel, niobium, and titanium; and a first overcoat layer disposed abovethe first barrier layer, wherein the first overcoat layer consists oftin, oxygen, and one of aluminum or magnesium.
 14. A film stack as inclaim 13, wherein the film stack is a transparent dielectric film stack,and wherein the film has an appearance that remains the same, by visualinspection, after a heat treatment.
 15. A film stack as in claim 14,wherein the aluminum or magnesium comprises less than 70% by weight ofthe total metal content of the composition of the second dielectriclayer.
 16. A film stack as in claim 13, wherein the second dielectriclayer consists of tin oxide doped with aluminum.
 17. A film stack as inclaim 13, wherein the second dielectric layer consists of tin oxidedoped with magnesium.